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1Departments of Psychiatry and 2Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania; and 3Department of Physiology and Neuroscience, Medical University of South Carolina, Charleston, South Carolina
Submitted 1 July 2005; accepted in final form 1 September 2005
Dopaminergic regulation of primate dorsolateral prefrontal cortex (PFC) activity is essential for cognitive functions such as working memory. However, the cellular mechanisms of dopamine neuromodulation in PFC are not well understood. We have studied the effects of dopamine receptor activation during persistent stimulation of excitatory inputs onto fast-spiking GABAergic interneurons in monkey PFC. Stimulation at 20 Hz induced short-term excitatory postsynaptic potential (EPSP) depression. The D1 receptor agonist SKF81297 (5 µM) significantly reduced the amplitude of the first EPSP but not of subsequent responses in EPSP trains, which still displayed significant depression. Dopamine (DA; 10 µM) effects were similar to those of SKF81297 and were abolished by the D1 antagonist SCH23390 (5 µM), indicating a D1 receptor-mediated effect. DA did not alter miniature excitatory postsynaptic currents, suggesting that its effects were activity dependent and presynaptic action potential dependent. In contrast to previous findings in pyramidal neurons, in fast-spiking cells, contribution of N-methyl-D-aspartate receptors to EPSPs at subthreshold potentials was not significant and fast-spiking cell depolarization decreased EPSP duration. In addition, DA had no significant effects on temporal summation. The selective decrease in the amplitude of the first EPSP in trains delivered every 10 s suggests that in fast-spiking neurons, DA reduces the amplitude of EPSPs evoked at low frequency but not of EPSPs evoked by repetitive stimulation. DA may therefore improve detection of EPSP bursts above background synaptic activity. EPSP bursts displaying short-term depression may transmit spike-timing-dependent temporal codes contained in presynaptic spike trains. Thus DA neuromodulation may increase the signal-to-noise ratio at fast-spiking cell inputs.
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